Incident Overview
On December 2, 2015, a Boeing 787-800 (Boeing 787-800) operating at Warsaw Chopin Airport (EPWA) experienced a brake system fault after taxiing. The flight crew received a "BRAKE CONTROLS FAULT" warning indicating issues with brakes 4 and 8. In response, the aircraft returned to the parking stand.
Troubleshooting and Repairs
Initial attempts to identify the cause of the fault were unsuccessful. The decision was made to replace the Electric Brake Actuator Control (EBAC) unit for brake assembly No. 4 (EBAC R OUTBD). However, this replacement did not clear the fault indication. Following consultations, a representative from the brake system manufacturer suggested replacing both brake assemblies No. 4 and No. 8. The subsequent replacement of the EBAC unit and brake assembly No. 4 resolved the problem. As recommended by the manufacturer, brake assembly No. 8 was also replaced.
Manufacturer's Assessment
According to the manufacturer, the root cause was an internal failure of one of the Electric Brake Actuators (EBA). Each brake assembly contains four EBA units. Similar incidents had been recorded previously where a single actuator malfunction led to a fault in the entire EBAC system.
Outcome
After the repairs, the aircraft operated on its subsequent scheduled flight without any further brake system issues. The investigation concluded that the incident was caused by an internal failure of one EBA actuator. No safety recommendations were issued by the commission.